Cytotoxic thymus-derived lymphocytes will be induced in vitro to a variety of haptens coupled to tumor target cells. Criss-cross experiments will be done to allow evaluation of the specificity of the cytotoxic effector cells. Anti-idiotypic antisera prepared against myeloma proteins specific for haptens will be tested as to their capacity to inhibit the activity of the cytotoxic effector cells specific for hapten coupled targets. This will show whether humoral antibody and thymus cell receptors may display identical idiotypes or not. Hapten coupled tumor cells will also be used to bring about sensitization of the immune system to tumor specific antigens.